Estimation of a Nusselt Correlations for Numerical Prediction of Frost Thickness Growth over a Cold Cylinder

2014 ◽  
Vol 875-877 ◽  
pp. 771-775
Author(s):  
Raquel da Cunha Ribeiro da Silva ◽  
Carlos T. Salinas ◽  
Kamal A.R. Ismail
Keyword(s):  
Numerical Solution ◽  
Experimental Studies ◽  
Optimization Method ◽  
Cylinder Surface ◽  
Frost Formation ◽  
Modeling Process ◽  
Numerical Predictions ◽  
New Correlation ◽  
Frost Layer Thickness ◽  
Frost Layer

This paper evaluates numerically some of the parameters involved in modeling the process of frost formation over a cold cylinder surface subject to the flow of humid air. Was utilized for numerical predictions the empirical Nusselt correlation from the literature, obtained in experimental studies on frost formation phenomena of frost grow over a cold cylinder surface. To predict frosting process a numerical solution was utilized, and a new correlation for Nusselt number based on the experimental correlation of Kim was estimated. For the new Nusselt correlation an optimization method that adjusts the numerical solution of modeling the frost formation process with experimental results of the frost layer thickness was used. The calculation procedure allows the estimation of the parameter K of equation. The modeling process was validated by comparison with available experimental data.

Frost Formation and its Density Behavior on Various Surfaces

2001 ◽  
Author(s):  
Cheolhwan Kim ◽  
Jongmin Shin ◽  
Alexei V. Tikhonov ◽  
Samchul Ha ◽  
Bongjun Choi
Keyword(s):  
Surface Energy ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Test Time ◽  
Test Results ◽  
Plate Temperature ◽  
Specific Test ◽  
Frost Formation ◽  
Frost Layer ◽  
Density Behavior

Abstract An experimental study has been conducted to investigate the effects of surface energy on frost formation. Test samples with three different surfaces of which Dynamic Contact Angles (DCA) are 23, 55 and 88 degrees are installed in a wind tunnel and exposed to a humid airflow. The thickness and the mass of frost layer are measured and used to calculate frost density while frost formation is visualized simultaneously with their measurements. Results show that frost density increases as time increases at specific test conditions. The air Reynolds number, the airflow humidity and the cold plate temperature are maintained at 12,000, 0.0042 kg/kg and −20 degrees Celsius, respectively. The surface with a lower DCA shows a higher frost density for a two-hour test, but no differences in frost density have been found after two hours of frost generation. Empirical correlations for thickness, mass and density are proposed as the functions of test time and surface energy. Visualization of frost generation was in good agreements with test results.

Experimental Studies of Adiabatic Flow Boiling in Fractal-Like Branching Micro-Channels

2008 ◽  
Author(s):  
Brian J. Daniels ◽  
James A. Liburdy ◽  
Deborah V. Pence
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Channel Length ◽  
Channel Height ◽  
Channel Network ◽  
Adiabatic Flow ◽  
Numerical Predictions ◽  
Micro Channels

Experimental results of adiabatic boiling of water flowing through a fractal-like branching microchannel network are presented and compared to numerical simulations for identical flow conditions. The fractal-like branching channel network had channel length and width ratios between adjacent branching levels of 0.7071, a total flow length of 18 mm, a channel height of 150 μm and a terminal channel width of 100 μm. The channels were DRIE etched into a silicon disk and pyrex was anodically bonded to the silicon to form the channel top and allowed visualization of the flow within the channels. The water flowed from the center of the disk where the inlet was laser cut through the silicon to the periphery of the disc. The flow rates ranged from 100 to 225 g/min and the inlet subcooling levels varied from 0.5 to 6 °C. Pressure drop across the channel as well as void fraction in each branching level were measured for each of the test conditions. The measured pressure drop ranged from 20 to 90 kPa, and the measured void fraction ranged from 0.3 to 0.9. The pressure drop results agree well with the numerical predictions. The measured void fraction results followed the same trends as the numerical results.

scholarly journals A New Spiral Potato Cleaner to Enhance the Removal of Impurities and Soil Clods in Potato Harvesting

2020 ◽  
Vol 12 (23) ◽  
pp. 9788
Author(s):  
Volodymyr Bulgakov ◽  
Simone Pascuzzi ◽  
Semjons Ivanovs ◽  
Zinoviy Ruzhylo ◽  
Ivan Fedosiy ◽  
...  
Keyword(s):  
Numerical Solution ◽  
Experimental Studies ◽  
Analytical Description ◽  
Potato Production ◽  
Angular Speed ◽  
Plant Residues ◽  
Agricultural Field ◽  
Production Chain ◽  
Removal Of Impurities ◽  
The Mathematical Model

Sustainability in the agricultural field suggests the conservation and maintenance of a natural environment of soil. Nevertheless, in the potato production chain, the mechanized harvest is carried out with the concurring removal of impurities and fertile soil. The authors have developed a new spiral potato cleaner which is able to capture and efficiently remove soil lumps of various sizes and shapes, as well as various plant residues. Theoretical and experimental studies have been performed on this soil clod cleaner to determine the structural and kinematic parameters that provide efficient capturing, motion and sifting down of the soil, through the gaps between the helices of its cleaning spirals. An analytical description of the motion of the clod of soil has been made and a system of differential equations has been compiled, whose numerical solution made it possible to determine the indicated reasonable operative parameters of the developed spiral potato cleaner. The results of the experimental research confirmed those ones obtained through the numerical solution of the mathematical model, i.e., rational angular speed ω of the rotation of the spirals from 20.0 to 30.0 rad s−1 and the radius R of spirals between 0.12 and 0.15 m.

scholarly journals Influence of Frost Growth and Migration in Cryogenic Heat Exchanger on Air Refrigerator

2019 ◽  
Vol 9 (4) ◽  
pp. 753 ◽  
Author(s):  
Shanju Yang ◽  
Zhan Liu ◽  
Bao Fu ◽  
Yu Chen
Keyword(s):  
Mass Transfer ◽  
Heat Exchanger ◽  
Numerical Model ◽  
Heat And Mass Transfer ◽  
Frost Formation ◽  
Transient Model ◽  
Transfer Rates ◽  
Low Humidity ◽  
And Migration ◽  
Frost Layer

Frost formation degrades the performance of heat exchangers greatly, thus influencing the cryogenic refrigerator. Different from frost formation on the evaporator surface, the growth and migration of frost layer inside the heat exchanger is of low temperature and humidity. In addition to the constantly changing boundary conditions, the effective prediction is difficult. In the present study, a numerical model was proposed to analyze the frost formation in the cryogenic heat exchanger of a reverse Brayton air refrigerator. Under small amounts of moisture, the growing of frost layer was simulated through the numerical heat and mass transfer by adopting semiempirical correlations. The frost formation model was inserted into the transient model of refrigerator, and numerical calculations were performed on heat and mass transfer rates, and growth and migration of frost layers in forced convection conditions. Experiments were conducted under different air humidity to investigate the frost formation and verify the numerical model. Through the model, the influences of frosting on the refrigerator were evaluated under different moisture contents and running time. It can be used to predict the performance of air refrigerators with low humidity and provide a basis for improving the system operation and efficiency.

On the RANS Modeling of Turbulent Airflow Over a Simplified Car Model

2011 ◽  
Author(s):  
G. Bella ◽  
V. K. Krastev
Keyword(s):  
Cfd Simulation ◽  
Aerodynamic Drag ◽  
Cooling System ◽  
Experimental Studies ◽  
System Optimization ◽  
Wake Flow ◽  
Car Model ◽  
Numerical Predictions ◽  
Light Duty Vehicle ◽  
Ahmed Body

The need for reliable CFD simulation tools is a key factor for today’s automotive industry, especially for what concerns aerodynamic design driven by critical factors such as the engine cooling system optimization and the reduction of drag forces, both limited by continuously changing stylistic constraints. The Ahmed body [1] is a simplified car model nowadays largely accepted as a test-case prototype of a modern passenger car because in its aerodynamic behavior is possible to recognize many of the typical features of a light duty vehicle. Several previous works have pointed out that the flow region which presents the major contribution to the overall aerodynamic drag, and which presents severe problems to numerical predictions and experimental studies as well, is the wake flow behind the vehicle model. In particular, a more exact simulation of the wake and separation process seems to be essential for the accuracy of drag predictions. In this paper a numerical investigation of flow around the Ahmed body, performed with the open-source CFD toolbox OpenFOAM®, is presented. Two different slant rear angle configurations have been considered and several RANS turbulence models, as well as different wall treatments, have been implemented on a hybrid unstructured computational grid. Pressure drag predictions and other flow features, especially in terms of flow structures and velocity field in the wake region, have been critically compared with the experimental data available in the literature and with some prior RANS-based numerical studies.

The Effect of Wake Passing on a Flow Separation in a Low-Pressure Turbine Cascade

2004 ◽  
Vol 126 (2) ◽  
pp. 250-256 ◽  
Author(s):  
Michael J. Brear ◽  
Howard P. Hodson
Keyword(s):  
Separation Bubble ◽  
Phase Locking ◽  
Experimental Studies ◽  
Leading Edge ◽  
Low Pressure ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Numerical Predictions ◽  
Unsteady Interaction ◽  
Wake Passing

This paper describes an investigation into the effect that passing wakes have on a separation bubble that exists on the pressure surface and near the leading edge of a low-pressure turbine blade. Previous experimental studies have shown that the behavior of this separation is strongly incidence dependent and that it responds to its disturbance environment. The results presented in this paper examine the effect of wake passing in greater detail. Two-dimensional, Reynolds averaged, numerical predictions are first used to examine qualitatively the unsteady interaction between the wakes and the separation bubble. The separation is predicted to consist of spanwise vortices whose development is in phase with the wake passing. However, comparison with experiments shows that the numerical predictions exaggerate the coherence of these vortices and also overpredict the time-averaged length of the separation. Nonetheless, experiments strongly suggest that the predicted phase locking of the vortices in the separation onto the wake passing is physical.

Droplet Coalescence in Liquid/Liquid Separation

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Weiwei E. ◽  
Kevin Pope ◽  
Xili Duan
Keyword(s):  
Relative Error ◽  
Volume Fraction ◽  
Force Balance ◽  
Water Volume ◽  
Droplet Coalescence ◽  
Liquid Separation ◽  
Water Separation ◽  
Numerical Predictions ◽  
New Correlation ◽  
Oil Water

Abstract In this paper, a new correlation is developed to predict liquid/liquid separation dynamics with a focus on a water/oil mixture. The correlation employs a force balance on the droplets to predict the rising velocity of the oil phase. The effect of droplet coalescence on the droplet's rising velocity is investigated, and the new correlation predicts the coalescence rate based on the oil/water volume fraction, as well as the initial droplet diameter. To develop the correlation for droplet coalescence, a series of new numerical simulations of a batch oil/water separation process were conducted. An equivalent experiment was conducted, the results of which agree well with the numerical predictions (relative error of 13.39%). The new correlation can predict the rate of separation with a relative error of 6.35% compared to numerical predictions.

Analysis and Optimization of Metal to Composite Joints for Marine Structures

2014 ◽  
Vol 556-562 ◽  
pp. 91-95
Author(s):  
Xiao Wen Li ◽  
Ping Li ◽  
Zhuang Lin ◽  
Dong Mei Yang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Mechanical Performance ◽  
Optimization Method ◽  
Additional Stress ◽  
Marine Structures ◽  
Hybrid Joint ◽  
Composite Joint ◽  
Numerical Predictions ◽  
Element Method

Composite to metal joints as important components of marine structures are gradually found in the marine industry. The purpose of this study is to investigate mechanical performance and optimization method of the composite sandwich to steel joints. The main emphasis was placed on the mechanical properties of a hybrid joint between a sandwich glass fibre reinforced plastic superstructure and a steel main hull. Based on the experiments of a base joint, a new finite element method was used to analyze a series of joints. The optimized joint was presented due to reducing weight and enhancing the mechanical performance. The numerical predictions of the base hybrid joint showed a very good correlation with the experiment results, which validated the reliability of the new finite element method. The strength of the optimized joint was also evaluated by finite element method. The result is similar to the base joint. And there is no additional stress concentration in weak parts. The optimized joint has 30% lower weight than the base joint, and the stress is only about 5% ~ 56% of the base one. The results of the present work imply that the change of geometric parameter is an effective method to improve the performance of the metal to composite joint.

Numerical Solution of Multidimensional Compressible Flow by High Order Nodal Discontinuous Galerkin Method

2013 ◽  
Vol 392 ◽  
pp. 100-104 ◽  
Author(s):  
Fareed Ahmed ◽  
Faheem Ahmed ◽  
Yong Yang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Numerical Solution ◽  
Finite Volume Method ◽  
Discontinuous Galerkin ◽  
Finite Volume ◽  
High Order ◽  
Numerical Predictions ◽  
Volume Method ◽  
Element Method

In this paper we present a robust, high order method for numerical solution of multidimensional compressible inviscid flow equations. Our scheme is based on Nodal Discontinuous Galerkin Finite Element Method (NDG-FEM). This method utilizes the favorable features of Finite Volume Method (FVM) and Finite Element Method (FEM). In this method, space discretization is carried out by finite element discontinuous approximations. The resulting semi discrete differential equations were solved using explicit Runge-Kutta (ERK) method. In order to compute fluxes at element interfaces, we have used Roe Approximate scheme. In this article, we demonstrate the use of exponential filter to remove Gibbs oscillations near the shock waves. Numerical predictions for two dimensional compressible fluid flows are presented here. The solution was obtained with overall order of accuracy of 3. The numerical results obtained are compared with experimental and finite volume method results.

Numerical Solution of Solid Propellant Transient Combustion

1979 ◽  
Vol 101 (2) ◽  
pp. 359-364 ◽  
Author(s):  
D. E. Kooker ◽  
C. W. Nelson
Keyword(s):  
Numerical Solution ◽  
Burning Rate ◽  
Solid Propellant ◽  
External Pressure ◽  
Finite Amplitude ◽  
Stable Model ◽  
Final State ◽  
Numerical Predictions ◽  
Numerical Solution Methods ◽  
Solution Methods

Three thermal theories of solid propellant combustion, [1, 2, 3], all based on the quasi-steady flame assumption, were subjected to a rapidly rising external pressure field simulating a gun combustion chamber. Transient burning rates were computed by four different numerical solution methods; the best results were obtained with an invariant imbedding scheme. The numerical predictions show that (1) burning rate “runaway” is a numerical difficulty and is not a solution to the models, (2) the final state of an intrinsically unstable model at constant pressure is composed of repeating finite-amplitude spikes, and (3) the dynamic burning rate from a linearly-stable model can be many times greater than r = apn.

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